Process for producing magnetic transducer with narrow sensing tip

ABSTRACT

A process for producing magnetic transducer comprising a relatively thin portion forming a sensing tip connected to a relatively thicker core portion including conductors wound around the core portion. The thin portion is separated in the region of its tip by a narrow gap filled with a material for forming a magnetic flux insulator.

United States Patent Farrand June 6,1972

[ PROCESS FOR PRODUCING MAGNETIC TRANSDUCER WITH NARROW SENSING TIP [72]Inventor: William A. Farrand, Fullerton, Calif.

[73] Assignee: North American Rockwell Corporation [22] Filed: July 14,1969 21 Appl. No.: 851,534

Related U.S. Application Data [62] Division of Ser. No. 623,385, Mar.15, I967, abandoned.

[52] U.S. Cl I56/309, 29/4729, 29/603, I 179/ 100.2 C [51] Int. Cl...C09j 5/00 [58] Field of Search 156/309, 322; 29/4729, 603; I 179/100.2 C

{56] References Cited UNITED STATES PATENTS 3,026,379 3/1962 Carpenter..29/603 3,139,680 7/1964 Scuro ..29/472.9

3 ,246,3 84 4/ I 966 Vice 3,079,470 2/1963 Camras l 79/ I 00.2

OTHER PUBLICATIONS Garrett et al. Broad Applications of DiffusionBonding, NASA Contractor Report 409, Mar. 1966, p. VIII.

Primary Examiner-Carl D. Quarforth Assistant Examiner-R. L. TateAttorney-William R. Lane, L. Lee Humphries and Robert G. Rogers 57]ABSTRACT A process for producing magnetic transducer comprising arelatively thin portion forming a sensing tip connected to a relativelythicker core portion including conductors wound around the core portion.The thin portion is separated in the region of its tip by a narrow gapfilled with a material for forming a magnetic flux insulator.

1 Claims, 4 Drawing Figures PATENTEBJUH 61972 INVENTOR.

WILLIAM A. FARRAND W95) (20 ATTOR N EY PROCESS FOR PRODUCING MAGNETICTRANSDUCER WITH NARROW SENSHIG TIP This is a division of applicationSer. No. 623,385, now abandoned, for A Magnetic Transducer with NarrowSensing Tip.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to a magnetic transducer and, more particularly, to'such atransducer having a relatively narrow sensing tip formed by individualthin elements connected over a relatively large area to a relativelythicker core element and separated in the region of their tips by anarrow (recording) gap comprising means forming a magnetic fluxinsulator.

2. Description of Prior Art Applicant is unaware of any magnetictransducer which anticipates the embodiments described herein, althoughvarious transducers are provided in order to meet the requirements ofthe present audio, video and data recording art. However, as therequirements for recording density increase, conventional transducerstructures become difficult to fabricate and use.

For example, as the requirement for increasing the density of tracks ofrecorded information increases, the recording tip must be made narrower.However, as the thickness of the transducers is reduced, the structuralstrength is also reduced. The transducers become fragile and difficultto wind with conductors. This difficulty is aggravated for the commonconfiguration in which toroidal winding is required. For large seals(multi-transducer) systems, uniformity of transducer per formance can beof paramount importance. In order to use a narrow pole tip -withoutmaterially affecting transducer uniformity, it is essential to haveaccurate control of pole face reluctance. Numerically small errors indimension on'a small pole face can produce large percentile changes inreluctance. ln addition to winding problems, fragile transducers aremore difiicult to aflix to transducer supports. On the other hand, ifthe tip portion is made larger, track density is decreased. A compromisedesign is usually selected which provides a transducer capable of beingproperly wound and connected to a transducer support. In such design,however, the recording density is relatively low.

A transducer is desired in which the recording tip can be maderelatively narrow to increase the recording track density but in whichstructural strength of the elements requiring winding is independent ofthe desired tip width and wherein the mounting problems are simplified.

SUMMARY OF THE INVENTION Briefly, the invention comprises a relativelythick magnetic core member on which windings may be placed for inducingor for sensing magnetic flux in the core. The core compriseselectrically insulated and adjacent members which are interconnected atone end. One simple configuration for this element is a horseshoe shapedintegral part which can be described as being the equivalent of threeattached parallelepipeds such that the cross-sectional area of each legis approximately square and equal. However, the precise shape may beadapted to the needs of a particular application.

A relatively thin magnetic portion (the pole pieces) is attached to thecore member to carry magnetic flux from the core to a recording gap in athin portion adjacent to the recording surface. The surfaces where thethin portion is attached to the core portion are relatively large andhave a relatively small gap separation between the core and thinportion. The large area, small gap joints between the core and the thinportion, have relatively low reluctance. Therefore, this structure formsa magnetic flux path which is of low reluctance except for the recordingor transducing gap. Either term may be used interchangeably in thesubsequent description.

The general profile shape of the thin pole piece element may be made inany of the forms conventionally used for producing such pole pieces inthe prior art. The recording gap may be formed with a material such asglass which has relatively little influence on the magnetic reluctanceof the gap, or

it may be filled with a high conductivity material such as a metal toproduce an eddy current shim. Such a shim behaves like a magnetic fluxinsulator during changes in flux. In either case an induced flux inpassing across the recording gap spread out (fringes) into the adjacentrecording medium and can, therefore, be used to modify the state ofmagnetization of said medium. Similarly, when a magnetic patternpreviously recorded on the medium is passed rapidly by the pole tip,some of the flux surrounding the magnetic pattern end picked up in thepole tips, follows the path through the pole tips and core instead ofacross the magnetic gap and, therefore, in-

duces current in the core windings. When the rapidity of flux 7 changeis sufficiently high, an eddy current shim improves the efficiency ofboth operations.

' In one embodiment the thin portion is attached at right angles to armmembers of the core. The'stru'cture is attached to a transducer supportso that the tip of the transducer is disposed adjacent to therecordingsurface for normal operations.

Therefore, it is an object of this invention to provide an improvedmagnetic transducer.

A still further object of this invention is to provide a magnetictransducer having a relatively thick core and relatively thin recordingtip.

Still another object of this invention is to provide a magnetictransducer having improved structural rigidity.

A still further object of this invention is to provide a magnetictransducer more easily attached to transducer supports.

Another object of this invention is to provide a magnetic transducerhaving a thin sensing tip for increasing recording density.

Another object of this invention is to provide a magnetic transducerwhich may be more easily wound than prior art devices.

A still further object of this invention is to provide a transducer inwhich precision control of recording gap geometry and resultantreluctance is readily attained.

A still further object of this invention is to provide a transducercomprising thin and thick portions in which the thin portion has a'recording gap filled with-a material for producing a magnetic fluxinsulator including the process for producing the gap- BRIEF DESCRIPTIONOF DRAWINGS FIG. 1 illustrates a preferred embodiment of a magnetictransducer attached to a transducer support wherein the pole tips areattached at right angles to the core arms.

FIG. 2 illustrates a second embodiment of a magnetic transducer whereinthe pole tips are attached tothe side of the core arms and areessentially coplanar therewith.

FIG. 3 illustrates the recording gap area of a modified pole tipconfiguration which permits a narrow recording tip to be combined with asomewhat thicker pole tip portion of the structure.

FIG. 4 illustrates an alternate configuration of the main core element.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows magnetic core 1comprising a rectangular shaped member having electrically insulated andseparated arm members 2 and 3 interconnected at one end. Inasmuch as theother end of the. rectangular shaped member is not connected, the coredoes not form a complete flux path. windings 4 and 4' are disposedaround the arms for inducing flux into the core and for sensing (byinduced EMF) flux changes induced in the core by, for example,information comprising part of data stored on a recording track. Thewindings are formed from conductors which may be bobbin wound ordirectly wound on the arm members before the transducer is assembled.

Relatively thin portion 7, divided into sections 10 and 10', forms apole piece for completing the magnetic circuit of the core. For theparticular embodiment illustrated, the sections are attached at rightangles to the ends of the arm members.

netic insulator in which case flux passes across the gap with thefringing flux Serving for recording (or reproducing). It may also be agood electrical conductor known as an eddy current shim. Such a shimbehaves like a magnetic insulator for rapidly changing flux and thusforces the useful flux to bypass the gap area-in which it is located. Asa result, the useful (gap fringing)'recording and reproducing fluxthrough the recording surface is increased.

Each of the sections comprising the thin portion is tapered from theareas connected to the arms of the main core to the gap for forming arecording tip having a relatively reduced height. A reduced gap heightis desirable so that the flux passing between the sections isconcentrated in the tip during readingand sensing. For example, a heightof 0.005 inches is considered to bea reasonable design value. The thinportion may have a width of approximately 0.005 inches. The core as wellas the thin portion may be comprised of a ferrite material or othermagnetic materials known to persons skilled in the 311.

Before the thin portion is attached to the core, the core is affixed tothe top surface of transducer support member 6. The support has a heightfor maintaining the transducer recording tip at a desired distance fromrecording surface 9 during operation. Raised inserts 8, 8', l3 and 13support the core above the top of the transducer support. Although notshown, the. support is usually connected to a positioning member. Inorder to'improve the mechanical strength of the completed transducer,particularly the thin portion, the inner surface. of the sectionscomprisingthe portion may be bonded or otherwise affixed to the outeredge of the transducer support A transducer support of the type shownand which can be used in the present invention is described andillustrated in patent application Ser. No. 606,204 filed on Dec. 30,1966 now abandoned for Fluid Bearing Fads for Supporting Transducers, byW. A. Farrand, et al.

A positioning member and other parts of a recording system with'whichthetransducer may be used are described in patent application Ser. No.394,976, now US. Pat. No. 3,359,549, for a Disc Memory by W. A. Farrand,et al., and for a Transducer Positioning Member Having HydrostaticBearing Supports, Ser. No. 607,444, now [1.8. Pat. No. 3,436,994 by W.A. Farrand, et al. v

Although specific examples of support, recording surfaces,

. positioning members, etc. are described in the referencedapplications, -itshouldbe understood that application of the transducerherein described isnot limited to such' a system configuration.

In one process the shim of the recording tip may be produced by coatingthe finely finished gap surface of the pole elements with a relativelythincoating of a metal such as silver or an insulating material such assilica or glass. Thereafter, the two faces may be placed in intimatecontact and furnace bonded either by actual melting of the shim materialor by diffusion bonding at a temperature below the melting point. Topermit high recording cell density along track, it is desirable that therecording gap be quite thin. The technique described permits controlofthis gap thickness in the range of a few microinches to a fewmilli-inches. Other more commonly used techniques, such as the use ofvitreous frit (conductive or nonconductive), for fusion bonding of thetwo halves or the use of I a vitreous melt drawn into the gap bycapillary action while it is mechanically clamped in'position, may alsobe used within the spirit of the present invention.

This pole tip configuration and assembly technique permits fabricationby a convenient method. Relatively long sticks" of appropriate magneticmaterial such as ferrite are formed to a cross section corresponding tothe pole element outline. These "sticks" are then bonded together as aunit (if desired, with non-magnetic fillers to provide a mechanicalstrut as submonly used in preparing semiconductor wafers and the like.

The slices so prepared may be inspected for defects and the good onesare immediately ready for final assembly to the main core and transducersupport. Prior to assembling the thin portion to the core, the ends ofthe arm members and the surface areas of the sections to be attached tothe arm members are lapped co-planar. The surfaces of the sections whichare attached to the ends of the armmembers comprise a large arearelative to the surface area of the sections on both sides of therecording gap. Asa result, the magnetic reluctance of the recording gapis large relative to the magnetic reluctance between the core and thethin portion.

Use of the stick assembly and slicing method of fabricationautomatically assures lateral alignment of the pole tips, one of thecritical factors in controlling transducer uniformity. It also aids incontrol of accuracy and uniformity of recording gap width and is ofadvantage in the conventional double C transducer forms as'well.

During recording, the tip may be separated from recording surface 9 by agap of microinches during normal operation so that the flux affects themagnetic orientation of the material comprising the recording track. Byvirtue of the thin tip structure and narrow recording gap previouslydescribed, it

is possible to increase both the density of computer bits (data isbonded to the side of the main core member rather than to the end. It,therefore, extends in a generally coplanar manner relative to the maincore. Alternatively, the ends of the main core member might by providedwith slots into which the pole member was bonded. Furthennore, it wouldbe possible to provide oblique ends on the main core member to which thepole member would be bonded, providing a configuration bent at an angleintermediate between the cases of FIG. 1 and FIG. 2. Except for meansprovided for mounting these alternative configurations to a transducersupport, the function of all elements shown in FIG.-2 is the same asdescribed'under FIG. 1. An exemplary flux pattern 5 isshownat the tip ofthe FIG. 2 embodiment passing into recording surface 9' FIG. 3illustrates a modified method for producing the recording gap portionsof the pole member for either of the previously described embodiments.Herein the main structure of the pole elements may be made somewhatthicker than the required tip width for both structural strength andlower mag netic reluctance. The element is reduced to minimum thicknessonly in the immediate neighborhood of the recording gap as shown at 16.If this thin portion extends only as far as indicated by the solid line17 in FIG. 3,, it is essential that an eddy current shim beused in therecording gap to take full advantage of the structure. If anonconductive shim is used, the thinning must be extendedback'beyond'the full depth of the recording gap region as shown in thedotted lines at 18.To take full advantage of the added strength providedin the pole element by this configuration, it is desirable that anonmagnetic strut 23 interconnected the portions of the pole tipelements. Such a strut should be of a material compatible in thermalexpansion and other structural characteristics with the pole tipmaterial. For example, if a magnetic ferrite is used for the pole tips,a nonmagnetic ferrite or other ceramic 'may be used to form a strut, orsupport. a

FIG. 4 illustrates a further alternate configuration of the main coremember. In this case the core is essentially straight rather thanhorseshoe'shaped and is configured like a conventional winding bobbinwith a reduced central portion 19 and larger end portions 20 (dumbbellconfiguration). The en-' larged end portions are of sufficient size topermit affixing the pole piece element to a flat side surface 21. By useof this configuration, the coil or coils may be wound directly on themain core element by conventional winding techniques. While notessential, it is desirable that the proportions of such a main coremember provide sufficient room for the necessary winding below the levelof the surface 21. Furthermore, if at least one other surface such as 22of the enlarged ends extends beyond the winding, it may be convenientlyused for attaching the main core to a transducer support.

As exemplified in the referenced applications, a transducer is connectedto a support disposed over a recording surface such as a recording disc,drum, etc. The support may be stationary or movable. A signal may directa drive means such as a motor to position the transducer at a particularrecording track. In addition, a current to the winding for recording abinary one or zero at the location may be provided. A plurality of suchrecording stages may be made before the transducer is re-positioned. Inthe alternative, a signal could direct the transducer to be positionedat a recording track for the purpose of reading infonnation previouslyrecorded at that location. The current induced by the recordedinformation could be processed by the arithmetic unit or by otherportions of the processing system connected to receive the information.

Although the invention has been described and illustrated in detail, itis to be understood that the same is by way of illustration and exampleonly, and is not to be taken by way of limitation; the spirit and scopeof this invention being limited only by the terms of the appendedclaims.

I claim: 1. A method for producinga magnetic transducer with a narrowsensing tip formed between adjacent pole faces, said method comprisingthe steps of,

coating at least one of the pole faces with a relatively thin layer ofsilver,

forcing the pole faces including the coating of silver together forforming a gap between the pole faces equal to the thickness of saidsilver coating,

subjecting the pole faces and the silver coating to a temperature belowthe melting point of the material comprising the pole faces and thesilver coating for diffusing the silver coating material and thematerial comprising the pole faces together thereby forming an intimatebond between the pole faces which are separated by a gap comprisingthesilver coating material.

